Black silicon solar thin-film microcells integrating top nanocone structures for broadband and omnidirectional light-trapping

Abstract

Recently developed classes of monocrystalline silicon solar microcells (µ-cell) can be assembled into modules with characteristics (i.e., mechanically flexible forms, compact concentrator designs, and high-voltage outputs) that would be impossible to achieve using conventional, wafer-based approaches. In this paper, we describe a highly dense, uniform and non-periodic nanocone forest structure of black silicon (bSi) created on optically-thin (30 µm) µ-cells for broadband and omnidirectional light-trapping with a lithography-free and high-throughput plasma texturizing process.With optimized plasma etching conditions and a silicon nitride passivation layer, black silicon µ-cells, when embedded in a polymer waveguiding layer, display dramatic increases of as much as 65.7% in short circuit current, as compared to a bare silicon device. The conversion efficiency increases from 8% to 11.5% with a small drop in open circuit voltage and fill factor.

Heterogeneously Integrated Optoelectronic Devices Enabled by Micro‐Transfer Printing

“…While various fabrication methods exist for the production of thin‐film single‐crystalline silicon including epitaxial growth on porous silicon and kerf‐less exfoliation by stress‐induced crack formation, schemes based on anisotropic wet chemical etching are of special interest due to their ability to generate a wide range of silicon thicknesses (e.g., ≈2–50 μm) from bulk wafers, without the need for additional silicon deposition steps. Suitable layouts yield microscale devices (i.e., microcells) in geometries that are compatible with transfer printing, as summarized in Figure .…”

“…Another surface morphology that offers attractive features for photon management utilizes density‐graded nanostructures (so‐called ‘black silicon’) for broadband and omnidirectional antireflection and absorption enhancement, as demonstrated recently with printed silicon microcells . Here, metal‐assisted wet chemical etching of microcells (≈5.7 μm thickness) with an inverted doping layout forms density‐graded rod‐like nanocolumns on the front surface .…”

“…Here, metal‐assisted wet chemical etching of microcells (≈5.7 μm thickness) with an inverted doping layout forms density‐graded rod‐like nanocolumns on the front surface . Another example uses HBr‐based ICP RIE to yield nanocone structures on 30 μm‐thick silicon microcells, where randomly dispersed oxide islands act as etch masks …”

Lithography-Free, Low-Cost Method for Improving Photodiode Performance by Etching Silicon Nanocones as Antireflection Layer

“…To improve the omnidirectional sensitivity within broadband wavelength, surface roughening and nanotexturing have been investigated [10][11][12][13][14]. Laser pulse irradiation in SF 6 environment [15] and self-mask reactive ion etching (RIE) [4,16] can produce subwavelength structures on silicon and suppress the optical reflection below 5%. However, most of these methods are too expensive and complex for industrial application and their nanostructure sizes are as large as hundreds of nanometers.…”

Effect of substrate temperature on the plasma texturing process of c‐Si wafers for black silicon solar cells

“…For instance plasmas based on different gas mixtures as SF 6 /O 2 [5], CF 4 [6], and SF 6 /N 2 [7] have been investigated, and, other techniques such as plasma immersion ion implantation [8], laser texturing [9], vertical silicon nanopillar arrays [10], nanowires [11], and nanocones [12]. However, the structures obtained by those techniques are needle-like, tip-like, wire-like, and sponge-like, which are not suitable for reliable c-Si surface passivation in solar cells.…”